Descriptions

Outline

Click the species name for a description of the organism

What is Histoplasma capsulatum?

Histoplasma capsulatum is the most common cause of fungal respiratory infections (histoplasmosis) in the world. While most infections are mild, 10% of cases result in life-threatening complications such as inflammation of the pericardium and fibrosis of major blood vessels (Durkin, Kohler et al. 2001). Once infected, a latent infection may be reactivated. Histoplasma poses a particular threat to the elderly and to immunocompromised patients (Rachid, Rezende et al. 2003).

Molecular characterization has shown that a number of fungi collectively known as H. capsulatum actually comprises seven phylogenetic species. There are two discrete phylogenetic species in Northern America: Histoplasma class I (NAm I) and Histoplasma class II (NAm II) (Kasuga, White et al. 2003). Sequence analysis shows that the two Northern American phylogenetic species are as distant from each other as from any other Histoplasma clade, which radiated 3-30 million years ago (Kasuga, White et al. 2003). In addition to these sequence differences, the two North American H. capsulatum show a key difference in virulence. While the NAm I strains are chiefly isolated only from AIDS patients, NAm II strains infect otherwise healthy individuals.

H. capsulatum sequencing is underway at Washington University for NAm II. Sequencing the closely related NAm I strain will clarify the genomic basis for the difference in virulence and interactions with the host immune system.

References

Rachid, A., L.S. Rezende et al. (2003). A case study of disseminated histoplasmosis linked to common variable immunodeficiency. Braz J Infect Dis. 7(4):268?272.

Durkin M, Kohler S, Schnizlein-Bick C, LeMonte A, Connolly P, Goldberg J, Garringer T, Wheat LJ. (2001) Chronic infection and reactivation in a pulmonary challenge model of histoplasmosis. J Infect Dis. 183(12):1822-4.

Kasuga T, White TJ, Koenig G, McEwen J, Restrepo A, Castaneda E, Da Silva Lacaz C, Heins-Vaccari EM, De Freitas RS, Zancope-Oliveira RM, Qin Z, Negroni R, Carter DA, Mikami Y, Tamura M, Taylor ML, Miller GF, Poonwan N, Taylor JW.(2003) Phylogeography of the fungal pathogen Histoplasma capsulatum. Mol Ecol. 12(12):3383-401.